Several benzodiazepines containing reactive functional groups were synthesized as specific, irreversible inhibitors of the benzodiazepine receptor in order to further study and characterize these receptors, through which the pharmacological properties of benzodiazepines are expressed. Binding studies using the alkylating benzodiazepine, kenazepine, strongly suggest the existence of several populations of benzodiazepine (BZ) receptors in the rat CNS. Kenazepine reacts non-competitively and irreversibly with some receptors and competitively (reversibly) with others. Cerebellum contains the largest proportion (ca. 80 percent ) of the non-competitive type, while hippocampus and cortex contain a preponderance of competitive type receptors (ca. 80 percent and 50 percent, respectively). The Hill coefficients for kenazepine are 0.7 in cortex and cerebellum, and near unity in dorsal hippocampus. Different populations of BZ receptors may mediate different physiologic and pharmacologic effects in vivo.